Time-resolved study of intense nanosecond laser-induced dense plasma dynamics beyond self-similar regime

Abstract Understanding the fundamental mechanisms underlying early-time laser induced plasma dynamics on solids is crucial for interpreting complex plasma expansion anomalies such as splitting, fragmentation, and detachment, which can hinder many practical plasma applications. In this study, we investigated the initial dynamics of nanosecond laser-induced plasma on a copper target in ambient air at laser intensity regime of ∼ GW/cm2. Time-resolved pump-probe reflectometry was employed as the primary experimental technique, supported by radiation-hydrodynamic simulations. The key experimental findings are intensity dependent sharp drop in the probe reflectivity and observation of novel anomalous modulations during the early stages of plasma evolution. These modulations, observed in the reflected probe signal during initial tens of nanoseconds (10 ns to 30 ns) of laser-plasma interaction, are of the order of 0.1 GHz. The experimentally observed intensity-dependent drop in the probe reflectivity matched well with the theoretical estimates, obtained with density and temperature profiles from radiation hydrodynamic simulations. Various possibilities about the physical origin of early-time anomalous modulations are discussed.